Influence of fluorine chemistry on supercritical fluid-fluid phase separations

Currently available studies on supercritical fluid phase separations are li mited to chemically nonreactive systems at low pressure. The present study is concerned with a possible influence of chemical reactions on a supercrit ical phase change above 1 Cpa. We will first give a brief review of statist ical mechanical theory, which is designed to handle chemically reactive sys tems, as used in this work. We next apply the theoretical formulation to ch emically reactive systems containing species composed of C, H, N, O, F atom s. These systems produce mixtures such as CO, CO2, H2O, N-2, HF, etc. Our e arlier calculations [1] without F atoms predicted that these molecular syst ems separate into an N-2-rich and an N-2-poor fluid phases at high pressure and high temperature. This prediction has been experimentally confirmed in part for a N-2+H2O mixture [2]. Addition of F atoms complicates the chemic al equilibrium, as the chemical species can react with ii or C atoms to pro duce HF and CF4 The chemical equilibrium calculations described below predi ct that fluorine occurs mostly as HF in the N-2-poor phase up to a certain pressure, beyond which it appears mostly as a constituent in CF4 in the N-2 -rich phase. But the shift in fluorine chemistry is sensitive to intermolec ular potentials involving HF and can be abrupt in thermodynamic sense, ther eby enhancing the character of the N-2-fluid phase change. Relevance of the present prediction to detonation properties of high explosives containing fluorine binders is discussed. (C) 2000 Elsevier Science B.V. All rights re served.